In a system that supplies fuel injected from a high-pressure pump to a fuel injection valve of each cylinder in an internal combustion engine, an injection quantity variation (air-to-fuel ratio variation) occurs between cylinders of the internal combustion engine. One method of correcting the variation is described in Patent Literature 1, for example. According to the method, a fuel pressure decrease caused by fuel injection of the fuel injection valve of each cylinder is calculated based on an output of a fuel pressure sensor for detecting the fuel pressure, as information on the injection quantity variation. Then, an injection pulse width of the fuel injection valve of each cylinder is corrected based on the fuel pressure decrease caused by the fuel injection of each cylinder, thereby correcting (for example, decreasing) the injection quantity variation of the fuel injection valve of each cylinder.
During a transient operation such as acceleration or deceleration of the internal combustion engine, when a required injection quantity varies with a change of the operational state of the internal combustion engine, the injection quantity of the fuel injection valve of each cylinder sequentially changes in the order of injection. Accordingly, the fuel pressure decrease caused by the fuel injection of each cylinder also changes in the order of injection. In such a case, since the fuel pressure decrease caused by the fuel injection changes due to the change of the injection quantity according to the change of the operational state of the internal combustion engine, the fuel pressure decrease caused by the fuel injection of each cylinder cannot accurately reflect the injection quantity variation of each cylinder. For this reason, in the transient operation such as acceleration or deceleration of the internal combustion engine, injection quantity variation correction to correct the injection quantity variation of the fuel injection valve of each cylinder is performed based on the fuel pressure decrease caused by the fuel injection of each cylinder. In this case, the injection quantity variation of each cylinder is not precisely corrected, which may lead to wrong correction of the injection quantity of each cylinder.
In the method described in Patent Literature 1, such a situation is not considered at all. Therefore, in the transient operation of the internal combustion engine, the fuel pressure decrease caused by the fuel injection of each cylinder cannot accurately reflect the injection quantity variation of each cylinder due to the change of the injection quantity according to the change of the operational state of the internal combustion engine. Moreover, injection quantity variation correction to correct the injection quantity variation of the fuel injection valve of each cylinder is performed based on the fuel pressure decrease caused by the fuel injection of each cylinder, which may lead to wrong correction of the injection quantity of each cylinder.